/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.mvc.condition;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

import javax.servlet.http.HttpServletRequest;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

/**
 * Implements the {@link RequestCondition} contract by delegating to multiple
 * {@code RequestCondition} types and using a logical conjunction (' && ') to
 * ensure all conditions match a given request.
 *
 * <p>When {@code CompositeRequestCondition} instances are combined or compared
 * they are expected to (a) contain the same number of conditions and (b) that
 * conditions in the respective index are of the same type. It is acceptable to
 * provide {@code null} conditions or no conditions at all to the constructor.
 *
 * @author Rossen Stoyanchev
 * @since 3.2
 */
public class CompositeRequestCondition extends AbstractRequestCondition<CompositeRequestCondition> {

    private final RequestConditionHolder[] requestConditions;


    /**
     * Create an instance with 0 or more {@code RequestCondition} types. It is
     * important to create {@code CompositeRequestCondition} instances with the
     * same number of conditions so they may be compared and combined.
     * It is acceptable to provide {@code null} conditions.
     */
    public CompositeRequestCondition(RequestCondition<?>... requestConditions) {
        this.requestConditions = wrap(requestConditions);
    }

    private CompositeRequestCondition(RequestConditionHolder[] requestConditions) {
        this.requestConditions = requestConditions;
    }


    private RequestConditionHolder[] wrap(RequestCondition<?>... rawConditions) {
        RequestConditionHolder[] wrappedConditions = new RequestConditionHolder[rawConditions.length];
        for (int i = 0; i < rawConditions.length; i++) {
            wrappedConditions[i] = new RequestConditionHolder(rawConditions[i]);
        }
        return wrappedConditions;
    }

    /**
     * Whether this instance contains 0 conditions or not.
     */
    @Override
    public boolean isEmpty() {
        return ObjectUtils.isEmpty(this.requestConditions);
    }

    /**
     * Return the underlying conditions (possibly empty but never {@code null}).
     */
    public List<RequestCondition<?>> getConditions() {
        return unwrap();
    }

    private List<RequestCondition<?>> unwrap() {
        List<RequestCondition<?>> result = new ArrayList<>();
        for (RequestConditionHolder holder : this.requestConditions) {
            result.add(holder.getCondition());
        }
        return result;
    }

    @Override
    protected Collection<?> getContent() {
        return (!isEmpty() ? getConditions() : Collections.emptyList());
    }

    @Override
    protected String getToStringInfix() {
        return " && ";
    }

    private int getLength() {
        return this.requestConditions.length;
    }

    /**
     * If one instance is empty, return the other.
     * If both instances have conditions, combine the individual conditions
     * after ensuring they are of the same type and number.
     */
    @Override
    public CompositeRequestCondition combine(CompositeRequestCondition other) {
        if (isEmpty() && other.isEmpty()) {
            return this;
        }
        else if (other.isEmpty()) {
            return this;
        }
        else if (isEmpty()) {
            return other;
        }
        else {
            assertNumberOfConditions(other);
            RequestConditionHolder[] combinedConditions = new RequestConditionHolder[getLength()];
            for (int i = 0; i < getLength(); i++) {
                combinedConditions[i] = this.requestConditions[i].combine(other.requestConditions[i]);
            }
            return new CompositeRequestCondition(combinedConditions);
        }
    }

    private void assertNumberOfConditions(CompositeRequestCondition other) {
        Assert.isTrue(getLength() == other.getLength(),
                "Cannot combine CompositeRequestConditions with a different number of conditions. " +
                        ObjectUtils.nullSafeToString(this.requestConditions) + " and  " +
                        ObjectUtils.nullSafeToString(other.requestConditions));
    }

    /**
     * Delegate to <em>all</em> contained conditions to match the request and return the
     * resulting "matching" condition instances.
     * <p>An empty {@code CompositeRequestCondition} matches to all requests.
     */
    @Override
    @Nullable
    public CompositeRequestCondition getMatchingCondition(HttpServletRequest request) {
        if (isEmpty()) {
            return this;
        }
        RequestConditionHolder[] matchingConditions = new RequestConditionHolder[getLength()];
        for (int i = 0; i < getLength(); i++) {
            matchingConditions[i] = this.requestConditions[i].getMatchingCondition(request);
            if (matchingConditions[i] == null) {
                return null;
            }
        }
        return new CompositeRequestCondition(matchingConditions);
    }

    /**
     * If one instance is empty, the other "wins". If both instances have
     * conditions, compare them in the order in which they were provided.
     */
    @Override
    public int compareTo(CompositeRequestCondition other, HttpServletRequest request) {
        if (isEmpty() && other.isEmpty()) {
            return 0;
        }
        else if (isEmpty()) {
            return 1;
        }
        else if (other.isEmpty()) {
            return -1;
        }
        else {
            assertNumberOfConditions(other);
            for (int i = 0; i < getLength(); i++) {
                int result = this.requestConditions[i].compareTo(other.requestConditions[i], request);
                if (result != 0) {
                    return result;
                }
            }
            return 0;
        }
    }

}
